Name
Environmental Biology--Mr. Nelson
Lab: The Compound Microscope
The human eye cannot distinguish objects much smaller than 0.1 mm in size. The microscope
is a biological tool that extends vision and allows observation of much smaller objects. The
most commonly used compound microscope has one eyepiece. Light reaches the eye after
being passed through the objects to be examined.
In this lab, you will learn the parts of a compound microscope and learn how to use and care
for microscopes.
Procedure:
Part A: Care of the Microscope
1. The microscope is a precision instrument that requires proper care. Always carry the
microscope with both hands, one hand under its base and the other on its arm.
2. When setting the microscope on a table, keep it away from the edge. If a lamp is attached to
the microscope, keep its cord out of the way. Keep everything not needed for microscope
studies off your table.
3. The lenses of the microscope cost almost as much as all the other parts put together. Never
clean lenses with anything other than the lens paper designed for this task.
4. Before putting away the microscope, always return it to the low-power setting. The highpower objective reaches too near the stage to be left in place safely.
Part B: Using the Microscope
1. Using newspaper, cut a lower case “e” from the text of an article. Do not use a headline.
1a. Place the letter “e” right side up on a clean slide. With a dropping pipet, place one or two
drops of water on the letter. This type of slide is called a wet mount. Hold the cover slip at
about a 450 degree angle to the slide and then slowly lower it. This will insure no air bubbles.
The figures below show these steps.
2. Show Mr. Nelson the perfect wet mount slide you create in this step. If your slide has no air
bubbles, Mr. Nelson will put a secret symbol in the box below.
Mr. Nelson Rules!
3. Place the slide on the stage and clip it into place. Move the slide so the letter is in the
middle of the hole in the stage. Use the coarse-adjustment knob to lower the low-power
objective to the lowest position. Always focus items using low power first.
4. Look through the eyepiece and use the coarse focus knob to focus the letter “e”. Use the
fine focus knob to sharpen the focus. Adjust the diaphragm setting for the best light.
5. To determine how greatly magnified the view is, multiply the magnification number found
on the eyepiece by the magnification number of the objective lens you are using (low, medium,
or high). Our eyepieces are clearly marked with a 10x, indicating that the eyepiece lens
magnifies the object 10 times larger. However, the objective lenses are marked with two
numbers. The magnification of the objective lenses on our microscopes is the number
following “DIN’.
For example: eyepiece (10x) X objective (10x) = 100x total magnification
Using the figures from your microscope, fill in the chart below.
ANSWER IN RED FONT
6. Place the letter “e” on the stage right side up (so it reads like a regular letter “e” when you
look at it) Now, look at the letter “e” under the microscope at low power. Describe how the
orientation of the letter “e” on the slide compares to the orientation when
viewed under the microscope. Example orientation words are; upside down,
inside out, frontwards, backwards, etc., NOT larger.
7. Look through the eyepiece at the letter “e”. Use your thumbs and forefingers to move the
slide slowly away from your body. Which way does your view of the letter move?
USE RED
FONT
Low Power
Medium Power
High Power
Eyepiece Lens
Magnification
Objective Lens
Magnification
Total
Magnification
8. Move the slide
to the right. In
which
direction does
the microscope
image move?
9. On the Microscope Drawings for Lab hard copy. Make a sketch of the letter
“e” as it appears under low power of the scope. Make sure to use our rules for
good microscope drawings.
Part C: Measuring with a Microscope
1. Because objects examined with a microscope usually are small, biologists use units of
length smaller than centimeters or millimeters for microscopic measurement. One such unit is
the micrometer, which is one thousandth of a millimeter. The symbol for micrometer is um.
1 mm = 1000 um
ANSWER IN RED FONT
2. You can estimate the size of a microscopic object by comparing it with the size of the
circular field of view. To determine the size of the circular field of view, place a plastic mm
rule on the stage. Use the low power objective to obtain a clear image of the divisions on the
ruler. Carefully move the ruler until its marked edge passes through the exact center of the
field of view. Determine the diameter of the field of view under low power in mm. Enter the
info below then convert mm to um.
Low power field of view=________ mm = _________um
3. Remove the plastic ruler and replace it with the wet mount of the letter “e”. Using low
power, compare the height of the letter with the diameter of the low power field of view.
Estimate as accurately as possible the actual height of the letter e in mm, then
convert to um.
Height of letter = ______________mm = _____________um
4. Now go back to your sketch of the letter “e” in Procedure B-9. Using the
method Mr. Nelson showed you in class, add the height of the letter, in um, to
your sketch.
5. Remove the slide and place the plastic ruler back under the microscope. You will now
determine the medium power field of view. (reminder-focus under low power before
switching to medium power). Record your info below.
Medium power field of view=___________ mm = ___________um
6. To determine the high power field of view, you will need to do a calculation.
step #1:
Magnification number
of the high power
objective lens
=
A
Magnification number
of the low power
objective lens
step #2: Diameter of low power
field of view
=
Diameter of high power field of view
A
Example:
step #1: If the magnification of your low power objective lens is 12x and that of your
high power objective lens is 48x then A = 4 (48/12 = 4).
step #2: If the diameter of the low power field of view is 1600 um, the diameter of the
high power field of view is 400 um (1600/4 = 400 um).
ANSWER IN RED FONT
7. Using the method from procedure 6, fill in the answer below.
High power field of view=___________mm = _________________um
8. Mr. Nelson has some prepared Ameoba slides in class. Get a slide and sketch
one Ameoba under low power on your Microcope Drawings for Lab hard copy
sheet Label your sketch properly and include the length of the Ameoba in um.
9. Now switch to medium power and sketch the same Ameoba on your
Microcope Drawings for Lab hard copy sheet. Label your sketch properly and
include the length of the Ameoba in um.
10. Now switch to high power and sketch the same Ameoba on your Microscope
Drawings for Lab hard copy sheet. Label your sketch properly and include the
length of the Ameoba in um.
11. Dry the microscope slide completely when you have finished your work. Check to see that
the low power objective is in place over the stage. Do not store the microscope under
medium or high power, as this protects objectives from possible damage. Wrap the cord
around the base and cover the microscope. When your area is completely neat, call Mr.
Nelson over to check your area and you will receive further instructions.
Analysis and Conclusion
1. How does the orientation of an image under a microscope compare to its orientation with
the naked eye.
2. Use your data to tell me the relationship between the diameter of the field of view and the
total magnification?